I would also tend to use multiple, high wattage wire wound ceramic resisters that will not break down. If you must use a resistor divider to earth, you must ensure that the current passed does not exceed this trip value (there will be leakage from other devices, so a divider must draw well under the trip value). Note that in Europe most mains systems are protected via leakage current trips 30mA is common, some are 100mA especially where 'leaky' systems regularly trip or where inductive loads are an issue. I would tend to use a transformer and be safe! It may loose some noise at the high end, but. Multiply all of your scope readings by this factor to get the actual line voltage. Mark the resistor divider's ratio on the outside of the box. You can't be too careful when messing with the power mains! You might also include a pilot light to indicate the box is plugged into the mains. Make sure you construct this box in such a way and seal it up so there is NO CHANCE of accidentally touching the Hot Wire. ( Not that you will be purpously & routinely touching the output terminals, but accidents and slip-ups do happen. 10:1, 15:1, 20:1 - but still provides a safe-to-touch voltage level on the output jacks. Also, select the resistor values so they have a low enough impedance to not affect your scope's accuracy, but are high enough that you are not burning up too much power in the upper resistor and creating a lot of unnecessary heat.ДЄs you will be multiplying all of your scope readings by the inverse of this ratio, choose a ratio which is easy to manipulate mentally - e.g.

Select a resistor divider ratio so you get an output voltage which is both safe to touch and suitable for your scope's input range.

Also route the Earth Ground lead of the line cord to another banana jack, or 5-way, on the enclosure. Then bring the bottom of the divider and the center tap of the divider out to 5-way binding posts or banana jacks. Connect the top and bottom of the resistor divider to a line cord with a correctly polarized plug. This is a simple resistor divider housed in a safe non-conductive project box. The best way to approach this is to make a resistive divider box. You must be very careful when measuring voltages on the mains, especially in your country where the voltages are absolutely deadly. Are there any other safety issues I have not realized? SAFETY: When I am measuring AC, I will be using the scope from its internal battery or with a isolating transformer (1:1) so that it is floating, meaning that there is no connection to earth ground. If that is true, it's also safe to measure voltage between two main lines (400V RMS), since the peak-to-peak would be about 112 volts? If I set the attenuation from the scope and probe to 10X, the voltage is 23 RMS and it is safe to measure? And yes the probes are rated for 1kV.

Since I live in Europe the mains here are 230 V 50 Hz I can't measure them directly.

So now I have this new DSO and the input rating is 400V peak to peak AC, so it can handle about 140V AC RMS? Not that I'm going to input that much there. I have used oscilloscopes to troubleshoot electronics problems and measure AC engine current spikes at startup, but I have no experience using them to measure high voltage levels and my experience is with old analog scopes. I know there is quite few discussions already on this topic, but since English isn't my first language, I though it better to get some more information about this.

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